>>> cp
<qgis._core.QgsVectorLayer object at 0x7f541c0e0348>

>>> cp.source()
u'dbname='work_viewtest' host=myhost port=5432 user='b' password='bxxxxxx' key='id' table="public"."v2_calculation_point" (the_geom) sql='

f = QgsFeature()
f.setGeometry(QgsGeometry.fromPoint(QgsPoint(123, 456)))
f.setAttributes([10, 100, "ref", -1])
cp.dataProvider().addFeatures([f])
(True, [<qgis._core.QgsFeature object at 0x7f539ffa33e0>])
cp.updateExtents()
cp.updateFields()

INSERT INTO v2_calculation_point (id, content_type_id
  , user_ref
  , calc_type
  , the_geom)
VALUES
  (DEFAULT, 10, 'ref', -1, ST_GeomFromText('POINT(123 456)',28992))
;

ERROR: insert or update on table "v2_calculation_point" violates
foreign key constraint "content_type_id_refs_id_522d7533"

cp.dataProvider().addFeatures([f])
(True, [<qgis._core.QgsFeature object at 0x7fcece585a68>])
f = QgsFeature()
f.setGeometry(QgsGeometry.fromPoint(QgsPoint(123, 555)))
f.setAttributes([77, 199, "ref-new", 5])
cp.dataProvider().addFeatures([f])
(True, [<qgis._core.QgsFeature object at 0x7fcece585b00>])